The present invention relates to a magnetic memory device and a method for fabricating the same, more specifically, a magnetic memory device using a spin injection-type magnetoresistive effect element and a method for fabricating the magnetic memory device.
Recently, as a rewritable nonvolatile memory a magnetic random access memory (hereinafter called an MRAM) including magnetoresistive effect elements arranged in a matrix is noted. The MRAM uses combinations of magnetization directions of two magnetic layers to memorize information and, to read the information, detects resistance changes (i.e., current changes or voltage changes) between the resistance with the magnetization directions of the two magnetic layers being parallel with each other and the resistance with the magnetization directions of the two magnetic layers being anti-parallel with each other.
As the magnetoresistive effect element forming the MRAM are known the GMR (Giant Magnetoresistive) element and the TMR (Tunneling Magnetoresistive) element. Of them, the TMR element, which provides large resistance changes, is noted as the magnetoresistive effect element to be used in the MRAM. The TMR element includes two ferromagnetic layers laid one on another with a tunnel insulating film formed therebetween and utilizes the phenomena that the tunnel current which flows between the magnetic layers via the tunnel insulating film changes based on relationships of the magnetization directions of the two ferromagnetic layers. That is, the TMR element has low element resistance when the magnetization directions of the two ferromagnetic layers are parallel with each other and has high element resistance when both are anti-parallel with each other. These two states are related to data “0” and data “1” to use the TMR element as a memory device.
As the method for writing in the magnetoresistive effect element, the method (current magnetic field writing method) of flowing current in two signal lines (e.g., a bit line and a write word line) which normally intersect each other and applying a synthetic magnetic field of magnetic fields generated from the signal lines to the TMR element to thereby change a magnetization direction of one of the ferromagnetic layer (free magnetization layer) corresponding to the applied magnetic field is generally used.
However, in this method, the electric power consumption and reliability depend on the generation efficiency of the synthetic magnetic field generated by the bit line and the write word line and the ease of inversion of the free magnetization layer to the external magnetic field. Especially, as the size of the magnetoresistive effect element is more diminished for higher memory density, the demagnetizing field of the free magnetization layer is increased, which increases the magnetization reversal magnetic field Hc of the free magnetization layer. That is, as the integration is higher, the write current is increased, and the electric power consumption is increased.
To solve this, the so-called clad structure, in which the surroundings of the bit line and the write word line except the surfaces opposed to the magnetoresistive effect element are shielded to concentrate the magnetic fluxes, is proposed. However, the magnetization reversal magnetic field of the free magnetization layer is increased in inverse proportion with the decrease of the size, and the conventional current magnetic writing method drastically increases the write current, which will really make the write difficult.
In writing data, current is applied to the bit line and the write word line to inverse the magnetization of the free magnetization layer of prescribed selected element by the synthetic magnetic fields. At this time, the current magnetic fields act on a number of non-selected elements connected to the bit line and the write word line the current was applied to. The elements in such state are defined as to be in half-selected state; the magnetization reversal tends to unstably take place, which is a cause for erroneous operations. In the MRAM with the select transistor connected to, the write word line for writing is necessary in addition to the bit lines and the word lines, which complicates the device structure and the fabrication process.
In view of this, recently, the spin injection magnetization reversal element is noted. The spin injection magnetization reversal element is a magnetoresistive effect element including two magnetic layers with an insulating film or a non-magnetic metal layer formed therebetween, as do the GMR element and the TMR element.
In the spin injection magnetization reversal element, when current is flowed from the free magnetization layer to the pinned magnetization layer perpendicularly to the film surface, the spin polarized conduction electrons flow from the pinned magnetization layer to the free magnetization layer to make the exchange interaction with the electrons in the free magnetization layer. Resultantly, torque is generated between the electrons, and when the torque is sufficiently large, the magnetic moment of the free magnetization layer is inverted from anti-parallel to parallel. On the other hand, when the current is oppositely applied, the effect of the action opposite to the above can inverse the magnetic moment from parallel to anti-parallel. That is, the spin injection magnetization reversal element is a memory element which can induce the magnetization reversal of the free magnetization layer by the current control alone to rewrite a memory state.
The spin injection magnetization reversal element, in which even when the element size is decreased, and the magnetization reversal magnetic field Hc is increased, the inversion current is decreased due to the effect of the decreased volume, is very advantageous to increase the capacity and decrease the electric power consumption in comparison with the current magnetic field writing element. Furthermore, no write word lines are necessary, which allows the device structure and the fabrication method to be simplified.
Related arts are disclosed in, e.g., Reference 1 (Japanese published unexamined patent application No. 2003-249630), Reference 2 (Japanese published unexamined patent application No. 2004-241672), Reference 3 (Japanese published unexamined patent application No. 2004-259913), Reference 4 (Japanese published unexamined patent application No. 2004-281599) and Reference 5 (Japanese published unexamined patent application No. 2005-094002).
However, in the magnetic memory device using the spin injection magnetization reversal element, the magnetization reversal of the free magnetization layer is induced by leakage magnetic field from interconnections near the magnetoresistive effect element.